1. Field of the Invention
The present invention relates to a unidirectional long fiber three dimensional fiber structure suitable for use as a fiber reinforced material formed complicated shape preform for a composite material used in aircraft and spacecraft structures, ships, and vehicles and the like, as well as a method of producing such a structure.
2. Description of the Related Art
Methods of producing unidirectional three dimensional fiber structures include methods in which long fibers are immersed in a resin and then subjected to drawing, and methods in which prepregs, formed by impregnating fibers with a resin and then semi curing the impregnated fibers, are laminated together. However, both of these methods require the use of a resin as a forming. If a resin is used, then the production process and production time frame is restricted by the need to manage the life of the resin being used, meaning handling of the resin material is rather difficult.
Needlepunch of layered fibers in a single dimension is also a possibility, although presently no consideration is given to intertwine the interface between fibers in a three dimensional manner, and consequently various problems arise such as cracking of the fiber structure following matrix impregnation, and an inability to achieve sufficient interlayer strength even after molding, meaning a good fiber reinforced preform cannot be obtained. These problems cannot be resolved with the inventions disclosed in Japanese Patent Publication No. Hei 6-39743, Japanese Patent Publication No. Hei 7-59783, or Japanese Patent Laid-Open Publication No. Hei 09-004661. Furthermore, as shown in the apparatus of Japanese Patent Laid-Open Publication No. Hei 11-050371, another possible method involves laying or winding a plurality of layers of woven members, tape members or braided members, and then using needlepunch to integrate the layers into a single unit, but even this method does not aim to intertwine the interface between fibers in a three dimensional manner, and because a weaving step is included before the preform is obtained, shortening the preparation time is problematic.
Furthermore, in a three dimensional fiber structure in which the fibers have been aligned unidirectionally without needlepunch, the fiber density is very high and the space between fibers is extremely narrow. Consequently when an attempt is made to impregnate the structure with a resin, the matrix impregnation is extremely poor, meaning long periods of time are required to ensure an adequate level of impregnation.
In addition, in the case of the production of a carbon-carbon composite in which the fibers are aligned unidirectionally, delamination can occur between carbon fibers during the baking process, causing cracks to appear in the product, and preventing a superior product from being obtained.